One-time programmable fuse arrays, for example, programmable read-only memories (PROMs), store various values in a Central Processing Unit (CPU) or System-on-a-chip (SoC). These stored values (also called fuse values) may relate to security keys, activation of various CPU/SoC features and functions such as cache memory size, etc. These fuse values are programmed using ultra high voltages (typically >2.2V), where the CPU may operate on a much lower voltage (e.g., 1.0V). In-Field-Programmable (IFP) fuse arrays are one-time programmable fuses that are also used for storing customer specific data (i.e., fuse values). A primary use for these IFP fuse arrays is to store specific security keys which phone devices use to function on their mobile carriers' network as well as for storing data which enables or disables any of the various functions and features of the SoC platform.
Manipulating such fuse values can unlock various features in a chip undesirably by overriding fuse values or customer security keys. One way of unlocking a processor (e.g., CPU) by disrupting fuse values is through voltage level manipulation. Voltages may be supplied from a motherboard, outside of the die and package, and are thus susceptible to manipulation through physical access of voltage pins. Changing supply voltages affects how much current can flow through a primary fuse cell as well as the reference fuse cell (which is used to develop the voltage differential at Sense Amplifier inputs), and also affect the sensing clock which controls how long the sense amplifier is enabled. This distorts the current values fed into the fuse sense amplifier as well as reduces the time required to develop the sense amplifier differential, which in turn corrupts the fuse values that are being read out.